You May Want to Avoid These Ingredients in Cannabis Oil Vape Cartridges | Leafly

In a 2017 study conducted at the Medical Marijuana Research Institute in Arizona, researchers looked at the byproducts produced when vaporizing cannabis oil. These popular cannabis thinning agents were studied:
Propylene glycol (PG or PPG)
Vegetable glycerin
Polyethylene glycol (PEG) 400
Medium chain triglycerides
These thinning agents were heated to 230°C (450°F), and scientists tested the resulting vapors to detect the presence of harmful compounds like formaldehyde, acetaldehyde, and acrolein.

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Thinning Agent Alternatives in Vaporizer Cartridges
Producers of vaporizer cartridges are making a mass exodus away from these thinning agents due to their health risks and the unpleasant taste they tend to carry. Instead, many are turning to terpenes as they help thin the oil while improving flavor. Others are using different extraction methods such as distillation to achieve an oil thin enough to be consumed in a cartridge without the need for additive thinners.